A better understanding of the cell surface molecules involved in development of the mammalian visual system and in outgrowth/regeneration of processes by visual neurons, such as retinal ganglion cells, would be of fundamental importance. Such knowledge would aid a rational approach to the study and possible treatment of injured retinal ganglion cells and their axons, which form the optic nerve. One cell surface molecule that appears to be involved in neuronal development and regeneration is Thy-1 glycoprotein, which is located on the surface of mammalian retinal ganglion cells. The Principal Investigator has demonstrated that the regeneration of processes (also termed neurites) by rat and mouse retinal ganglion cells is enhanced by specific monoclonal antibodies against Thy-1. Most importantly, in preliminary experiments the P.I. has gathered evidence for a "naturally-occurring" binding site or receptor for Thy- 1, located on astrocytes, that enhances the regeneration of retinal ganglion cell processes; this is not surprising since the endogenous Thy-1 receptor is, in some respects, a structural analogue of exogenous antibodies against Thy- 1. Using anti-idiotype antibodies against Thy-1 antibodies, tentative identification of the Thy-1 receptor has been made using a combination of biochemical and molecular techniques. In these experiments, the anti-idiotype antibodies serve as probes that should structurally resemble antigenic sites on Thy- 1 since both bind to antibodies against Thy-1. The current grant proposes to further characterize this endogenous Thy-1 receptor. The work will primarily use molecular biological methods, but it will also be complemented by parallel biochemical and immunohistochemical studies. The Specific Aims of this proposal are -- 1. To identify and sequence a Thy- 1 receptor cDNA and map its chromosomal location. 2. To examine the synthesis, distribution, and expression of Thy- 1 receptor in vitro and in vivo. 3. To study the effect of Thy- 1 receptor on the outgrowth of rodent retinal ganglion cells in culture using (a) purified receptor, (b) transfected receptor cDNA into cell lines, and (c) antisense oligonucleotides to Thy- 1 receptor to down-regulate its expression on astrocytes. 4. To identify possible Thy- 1 receptors in other species in retina/optic nerve and elsewhere in the brain.